feat(web): animate zoom toggle with cubicOut easing

web/src/lib/actions/zoom-image.ts

@@ -9,14 +9,15 @@ export const zoomImageAction = (node: HTMLElement, options?: { disabled?: boolea
     zoomInstance.subscribe(({ state }) => assetViewerManager.onZoomChange(state)),
   ];
 
-  const stopIfDisabled = (event: Event) => {
+  const onInteractionStart = (event: Event) => {
     if (options?.disabled) {
       event.stopImmediatePropagation();
     }
+    assetViewerManager.cancelZoomAnimation();
   };
 
-  node.addEventListener('wheel', stopIfDisabled, { capture: true });
-  node.addEventListener('pointerdown', stopIfDisabled, { capture: true });
+  node.addEventListener('wheel', onInteractionStart, { capture: true });
+  node.addEventListener('pointerdown', onInteractionStart, { capture: true });
 
   node.style.overflow = 'visible';
   return {
@@ -27,8 +28,8 @@ export const zoomImageAction = (node: HTMLElement, options?: { disabled?: boolea
       for (const unsubscribe of unsubscribes) {
         unsubscribe();
       }
-      node.removeEventListener('wheel', stopIfDisabled, { capture: true });
-      node.removeEventListener('pointerdown', stopIfDisabled, { capture: true });
+      node.removeEventListener('wheel', onInteractionStart, { capture: true });
+      node.removeEventListener('pointerdown', onInteractionStart, { capture: true });
       zoomInstance.cleanup();
     },
   };

web/src/lib/components/asset-viewer/photo-viewer.svelte

@@ -103,7 +103,8 @@
   };
 
   const onZoom = () => {
-    assetViewerManager.zoom = assetViewerManager.zoom > 1 ? 1 : 2;
+    const targetZoom = assetViewerManager.zoom > 1 ? 1 : 2;
+    assetViewerManager.animatedZoom(targetZoom);
   };
 
   const onPlaySlideshow = () => ($slideshowState = SlideshowState.PlaySlideshow);

web/src/lib/managers/asset-viewer-manager.svelte.ts

@@ -2,6 +2,7 @@ import { canCopyImageToClipboard } from '$lib/utils/asset-utils';
 import { BaseEventManager } from '$lib/utils/base-event-manager.svelte';
 import { PersistedLocalStorage } from '$lib/utils/persisted';
 import type { ZoomImageWheelState } from '@zoom-image/core';
+import { cubicOut } from 'svelte/easing';
 
 const isShowDetailPanel = new PersistedLocalStorage<boolean>('asset-viewer-state', false);
 
@@ -21,6 +22,7 @@ export type Events = {
 
 export class AssetViewerManager extends BaseEventManager<Events> {
   #zoomState = $state(createDefaultZoomState());
+  #animationFrameId: number | null = null;
 
   imgRef = $state<HTMLImageElement | undefined>();
   isShowActivityPanel = $state(false);
@@ -45,6 +47,7 @@ export class AssetViewerManager extends BaseEventManager<Events> {
   }
 
   set zoom(zoom: number) {
+    this.cancelZoomAnimation();
     this.zoomState = { ...this.zoomState, currentZoom: zoom };
   }
 
@@ -69,7 +72,35 @@ export class AssetViewerManager extends BaseEventManager<Events> {
     this.#zoomState = state;
   }
 
+  cancelZoomAnimation() {
+    if (this.#animationFrameId !== null) {
+      cancelAnimationFrame(this.#animationFrameId);
+      this.#animationFrameId = null;
+    }
+  }
+
+  animatedZoom(targetZoom: number, duration = 300) {
+    this.cancelZoomAnimation();
+
+    const startZoom = this.#zoomState.currentZoom;
+    const startTime = performance.now();
+
+    const frame = (currentTime: number) => {
+      const elapsed = currentTime - startTime;
+      const linearProgress = Math.min(elapsed / duration, 1);
+      const easedProgress = cubicOut(linearProgress);
+      const interpolatedZoom = startZoom + (targetZoom - startZoom) * easedProgress;
+
+      this.zoomState = { ...this.#zoomState, currentZoom: interpolatedZoom };
+
+      this.#animationFrameId = linearProgress < 1 ? requestAnimationFrame(frame) : null;
+    };
+
+    this.#animationFrameId = requestAnimationFrame(frame);
+  }
+
   resetZoomState() {
+    this.cancelZoomAnimation();
     this.zoomState = createDefaultZoomState();
   }